The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In a wireless network, a transmitter communicates with a receiver by transmitting a signal to the receiver through a communication link or signal path, also commonly referred to as a “channel”. The communication link or signal path between a transmitter and a receiver can be represented by an effective channel, H. The effective channel represents the combined effect of signal deflection due to obstacles (hills, walls, and so on), scattering, fading, and power decay due to the distance between a transmitter and a receiver. If either the transmitter or receiver is in motion, the effective channel will be constantly changing. Further, other obstacles in the signal path that affect the channel may be moving. A conventional receiver is typically configured with an equalizer that attempts to undo effects on a signal caused by the channel that carries the signal, therefore, the effective channel is continuously determined to allow effective communication even when one or both of the transmitter and receiver are moving. The quality of the output data produced by the receiver is dependent upon accurately determining the effective channel.
One way to estimate an instantaneous effective channel between a receiver and a transmitter is for the transmitter to transmit a known pilot sequence. The pilot sequence can be inserted in predetermined positions in frames of data-carrying signals from the transmitter. The receiver determines the effective channel H based on characteristics of the pilot sequence. Accordingly, an equalizer can utilize the effective channel H to compensate for the effects of the channel on a received signal. Channel estimation and equalization may be implemented in either the time domain (e.g., pre FFT) or the frequency domain (e.g., post FFT). In orthogonal frequency domain multiplexed (OFDM) communication systems, channel estimation and equalization are performed in the frequency domain.